Method of heat exchange and evaporation

ABSTRACT

The invention provides an evaporation process and apparatus for an aqueous solution containing dissolved solids, such as mineral salts, without adherence of the solids to any surface contacting the aqueous solution. Heated immiscible oil is used as the heat transfer liquid which makes liquid/liquid contact with the solution, preferably in the form of a highly dispersed mixture of the solution and oil from a cooler part of the system in a mixing chamber whereby the solution droplets are vaporized by intimate contact with the hot oil. The mixture of hot oil and aqueous solution is fed from the mixing chamber into an evaporation chamber wherein all or a portion of remaining aqueous solution is converted to vapor by cascading downward over baffles, and the solids and liquid components of the mixture are separated into strata in the lower portion of the evaporating chamber. The oil stratum is continuously withdrawn, most of it being re-cycled to the heating and evaporation zones. The aqueous solution stratum is continuously withdrawn and re-cycled to the original evaporation step or on to a second stage evaporation step if so desired. The solids slurry is removed separately for separation of solids from liquids in a suitable solids-liquid separator. Apparatus surfaces exposed to the aqueous solution including particularly the mixing chamber, the heating elements in the oil heating chamber, and the evaporation chamber and parts therein are coated with a material which is preferentially oil wettable and zero water adsorbent. The immiscible oil circulating through the mixing chamber and evaporation chamber wets the surfaces therein, preventing adherence of solids and acting as a flushing agent to prevent sedimentation of solids thereon. All contacting apparatus surface is exposed to the aqueous solution should be smooth and free from sharp edges and should, preferably, be preferentially oil wettable. Multiple stage evaporators (details not shown) utilizing the methods herein disclosed may be used in order to conserve heat and selectively separate mineral components where feasible.

United States Patent 1 1 Erwin June 24, 1975 1 1 METHOD OF HEAT EXCHANGE AND EVAPORATION [75] Inventor: Ransome W. Erwin, Ogden, Utah [73] Assignee: Austral-Erwin Engineering Co.

[221 Filed: Nov. 14, 1972 1211 Appl. No.: 306,183

[52] US. Cl 159/47 R; 159/1 R; 159/13 R; 159/28 R; l59/DIG. l3; l59/D1G. 17;

[51] Int. Cl B0lb B0ld 3/34', BOld 19/00; B0ld l/OO; 801d 3/00; B01d l/22', F28f 13/18 [58] Field of Search l59/D1G. l7, 1 RW, 28 R, 159/28 B, 13 R, 13 A, 15,31, D 13; 165/133,

14 V, 203/7, 100, 100 DC; 202/158, 234,

[56] References Cited UNITED STATES PATENTS 199,785 1/1878 Borgin 55/206 2,431,820 12/1947 Montgomery..... 165/142 2,903,243 9/1959 165/108 X 3,050,786 8/1962 St John et a1. 165/133 3,232,847 2/1966 Hoff r. 203/11 3,298,932 1/1967 Bauer r 203/11 3,318,805 5/1967 Hess et a1. 159/D1G. 17 3,323,575 6/1967 Greenfield 159/13 A 3,325,400 6/1967 Hess ct a1. 159/D1G. 17 3,350,299 10/1967 Hess ct a1. 159/D1G. 17 3,370,636 2/1968 Francis, Jr. et a1. 159/31 X 3,392,089 7/1968 Guptill. Jr. et a1... 203/7 3,394,055 7/1968 Ludwig 159/D1G. 17 3,41 1,992 1 H1968 Mitchell 203/1 1 3,486,987 12/1969 Kassel et a1... 203/11 3,489,209 1/1970 Johnson 165/133 3,502,141 3/1970 Allen 165/133 3,741,878 6/1973 Osdor 159/D1G. 17 X Primary Examiner-Jack Sofer [57] ABSTRACT The invention provides an evaporation process and l conacxsm BIL-SOLUTION II III? FLIIP l tEllT GAS 011 STHI Hill!!! 57 51' 2 soumoli CYCLE some: cow if :2 1m c-mncusur SOLUHOI rm 4: w m m apparatus for an aqueous solution containing dissolved solids, such as mineral salts, without adherence of the solids to any surface contacting the aqueous solution. Heated immiscible oil is used as the heat transfer liquid which makes liquid/liquid contact with the solution, preferably in the form of a highly dispersed mixture of the solution and oil from a cooler part of the system in a mixing chamber whereby the solution droplets are vaporized by intimate contact with the hot oil. The mixture of hot oil and aqueous solution is fed from the mixing chamber into an evaporation chamber wherein all or a portion of remaining aqueous solution is converted to vapor by cascading downward over baffles, and the solids and liquid components of the mixture are separated into strata in the lower portion of the evaporating chamber. The oil stratum is continuously withdrawn, most of it being re-cycled to the heating and evaporation zones. The aqueous solution stratum is continuously withdrawn and re-cycled to the original evaporation step or on to a second stage evaporation step if so desired. The solids slurry is removed separately for separation of solids from liquids in a suitable solids-liquid separator. Apparatus surfaces exposed to the aqueous solution including particularly the mixing chamber, the heating elements in the oil heating chamber, and the evaporation chamber and parts therein are coated with a material which is preferentially oil wettable and zero water adsorbent. The immiscible oil circulating through the mixing chamber and evaporation chamber wets the surfaces therein, preventing adherence of solids and acting as a flushing agent to prevent sedimentation of solids thereon.

All contacting apparatus surface is exposed to the aqueous solution should be smooth and free from sharp edges and should, preferably, be preferentially oil wettable. Multiple stage evaporators (details not shown) utilizing the methods herein disclosed may be used in order to conserve heat and selectively separate mineral components where feasible.

5 Claims, 5 Drawing Figures VAPORIIATION z |1 Eunumco n u uuuw scnuuin 73 T 20 I 17 cLul stun um 46 IlXlNG CNAIIER r i z s may 5 mm cAscAmNG IEIOl/(O Ull VES$5L\ no sotunon nu OIL nwn zuo sues mu sotunon ro znn sues ,llFlLL nor RECYCLED) I OIL mu SOLUTIOh nruovto non stunm yo no sue: on arcvcirn METHOD OF HEAT EXCHANGE AND EVAPORATION ESSENCE OF THE INVENTION The invention relates to an improvement in the method of evaporating an aqueous solution containing dissolved solids to prevent adherence of precipitated solids to the contacting surface of the apparatus in which the method is carried out; which improvement consists in that the evaporation of the solution takes place in apparatus whose hot contacting surface is preferentially oil wettable and zero adsorbent of water from the solution while continuously wetting the contacting surface with an organic liquid which is immiscible with the aqueous solution being evaporated, said contacting surface comprising a fluorocarbon polymer.

The use of preferentially oil wettable surfaces in emulsion treaters is old as shown in my prior US. Pat. No. 3,903,243 discussed more fully hereinafter, but such surfaces are not substantially zero water adsorbent, a feature which I have now found to be essential to the prevention of adherence of precipitated solids to the hot contacting surface of an evaporator for aqueous solutions containing dissolved solids. More specifically, l have now found that by using a contacting surface comprising a fluorocarbon polymer, while continuously wetting the contacting surface with an organic liquid which is immiscible with the aqueous solution being evaporated adherence of precipitated solids to the contacting surface is avoided.

BACKGROUND OF INVENTION Because of its enormous scope in virtually all industrial processes, any significant improvement in heat transfer from one fluid to another and evaporation of aqueous liquids cannot help but be of utmost importance to most industries. Such improvement is concerned with innumerable processes, some of which are: making good water from seawater and brackish water, salvaging the mineral content, if possible; converting industrial waste waters to potable water. Salvaging the contaminants, if possible; converting radioactive atomic waste waters to solids which may be more readily isolated or stored in harmless areas than is possible with liquids; evaporating juices such as in the cane and beet sugar industry more efficiently with consumption of less energy for such; converting acidic mine wa ters to harmless solids, salvaging the water and valuable mineral content; converting brines, such as Great Salt Lake, into fresh water and valuable mineral contituents; and workable heat transfer systems to utilize steam power and recover valuable mineral contents from steam and brine produced by natural geothermal wells. In all of the aforementioned processes, the fouling of heat transfer surfaces and surfaces of confining vessels and the prevention thereof is astronomical in cost in manpower, maintenance, downtime, and low energy efficiency. This invention offers a novel, practicable means and method for prevention of such surface contamination without need of expensive and elaborate chemical treatment. together with novel means and methods for handling and separation of difficult mixtures of solids, liquids and gases.

In my US. Pat. No. 2,903,243, granted Sep. 8, 1959, is disclosed my discovery that precoating a heating element with a preferentially oil wettable material such as a silicone, epoxy resin, or phenolic resin prevented the adherence of insoluble calcium carbonate and other precipitates to the element when heating a mixture of crude petroleum and mineralized water, wherein the element was continuously exposed to an oil wash. Even though these coating materials proved fully effective in scale prevention at relatively high temperatures where no boiling occurred in heat treating crude petroleum emulsions, I later learned they would not apply to systems boiling mineralized waters. I also found that the reason the abovementioned coating materials would not prevent scaling at boiling temperature was because they adsorb water after prolonged contact with it, and become water wettable and susceptible to solids adherence. This is very prevalent when saturation is reached, and soluble salts are precipitated. Most industrial plastics such as epoxy resins, phenolic resins, polyethylene, neoprene, and the silicones are generally regarded as being preferentially oil wettable, but since they all adsorb traces of water upon prolonged contact with it, they eventually become oil repellant when immersed in a water environment, becoming water wettable and subject to solids adherence. Although I am not familiar with all industrial plastics, I have found only the fluorocarbon resins such as Duponts Teflon to be substantially zero water adsorbent and permanently water repellant when immersed in water indefinitely. I would presume pure gold to also be zero water adsorbent, since it has been found that a thin gold coating will render steam condensing tubes permanently water repellant and subject to dropwise condensation. In view of the foregoing, I have discovered that zero water adsorbent coatings such as the fluorocarbons, particularly DuPonts hexafluoropropylenetetrafluoroeothylene with the tradename FEP, retain their preferentially oil wettable properties in indefinite contact with boiling brines, and that their wetting with oil effectively prevents adherence of any precipitated salts to their surface. I also tried similar tests, using an oil wash, with phenolic resin and epoxy resin coated heating tubes and found the salt growth on them to be quite rapid, as much as Iain. salt thickness on a lin. diameter tube in 8 hours boiling of brine. FEP coated heating elements also salted up in boiling brine when no oil was present in the system. The teaching in my US. Pat. No. 2,903,243 and other patent art to the present time, and in technical literature in general, is not sufficient to enable technicians to boil brines or mineralized waters without scaling, even though the so-called preferentially oil-wettable materials listed in US. Pat. No. 2,903,243 are used with oil. If it were so, this means would have been employed years ago to cope with this very serious problem. Only in comparatively recent work, embodied in this and companion applications, have I discovered that the vital key is the use of substantially zero water adsorbent coatings, rather than the general run to temporarily oil wettable coatings. A chief discouraging factor in the use of fluorocarbon coatings on metallic heat exchanger tubes has been the prohibitive cost and difficulties in achieving good, permanent coatings; so difficult that industrial coaters shy away from doing such. Pure, small diameter, comparatively thick walled 10 mils) bundles of teflon tubes are in use for corrosive fluids, but they do not teach the use of oil films with them to prevent fouling. A metallic thin walled tube with a very thin coating of fluorocarbon (range of 0.5 to 2 mil thickness) is best for efficient heat transfer. Because of urgent need for such a tube to effect the method disclosed in this application and companion applications, I have perfected an economical means of heat bonding a coating of DuPont FEP to a metal surface which is strongly bonded and substantially permanently zero water adsorbent, and suitably thin. This method is the substance of my pending application No. 4l,375. I believe the novel disclosures on new and important uses for the basic methods described in U.S. Pat. No. 2,903,243 in this application. together with my discovery that substantially zero water adsorbent materials are essential to boiling of mineralized waters, are distinct and major improvements over the teaching of U.S. Pat. No. 2,903,243. I further believe that they will prove to be vital elements in solving some of the presently unsolved very serious problems in a broad spectrum of industry.

The objects and advantages of this invention are as follows: Provision of method and apparatus to:

1. Exchange heat with maximum continuous efficiency between two fluid systems through a permanently oil wettable wall without deposition of solids on the wall, wherein one of the fluids is, substantially, a mixture of oil and aqueous solution, and the other fluid may be liquid or gas or both, containing oil if solids are present,

2. Efficiently and economically evaporate waters containing dissolved and/or suspended solids to any desired extent including total dryness; recovering both the solids and water vapor or only either, if desirable; all, without fouling of the heating and evaporating system with mineral scale or solids.

3. Accomplish (l) and (2) without chemical treatment to prevent fouling of heat transfer surfaces thereby eliminating chemical costs and expensive chemical control.

4. To convey or circulate liquids containing dissolved or suspended solids without deposition of solids on the contacting surfaces thereby avoiding expensive shutdown time for clean-outs.

5. To heat, cool or evaporate extremely corrosive liquids, acidic or alkaline, in (l) and (2).

6. To accomplish (2) in multi-stage or vapor compression distillation if required thereby conserving energy.

7. Provide a novel, permanently oil wettable heat exchanger tube design for heating mixtures of oil and so]- ids-forming aqueous solutions. Wherein a vertically disposed tube is attached to the exchanger header at one end only, permitting uninhibited thermal expansion when heated; avoiding sedimentation common to horizontally disposed heat exchangers and vertical heat exchangers with conventional headers at each end of the tubes; permitting simple removal of the tube bundle from the top of the heating vessel without drainage of the vessel. Further provide an inner return condensate tube inside the heat exchanger tube with a unique arrangement of sizing that permits complete and continuous removal of liquid condensate from the lower portion of the heat exchanger tube with a negligible loss of vapor assuring maximum heat transfer efficiency with constant condensate removal.

8. Enhance heat transfer by the method of injecting inert gas or steam into the heat transfer zone outside the heating tube, wherein the injected gas increases the flow velocity of the circulating liquid and disrupts stagnant, insulating films on the heater tube, increasing heat transfer rate as much as 80 percent thereby greatly reducing the size requirement for expensive equipment.

9. Prevent salt buildup in and seizing of pump with water wettable interiors when circulating oil is contaminated with salts and brine, by injection of fresh water into the oil stream to the pump suction in amounts as small as one part of water to 3000 parts of oil; thus avoiding the need for a very expensive step of complete cleansing of the oil prior to pumping, or the alternative expense of providing of permanently oil wettable interiors for the pump.

10. Feed an aqueous solution (brine etc.) to a circulating hot oil as a highly dispersed mixture composed of the solution and oil from a cooler part of the system, this mixture being effected by a mixing pump; with oil being the continuous phase of the mixture in order to facilitate complete mixing with the circulating hot oil when combined with it, which, in turn, provides thorough dispersion of the solution droplets throughout the hot circulating oil without the added cost of having to subject the hot circulating oil to mixing with the aqueous solution in a pump with attendant vapor lock problems; the purpose of the whole procedure being to more efficiently vaporize the solution droplets by intimate contact with the hot oil with minimum pump size.

11. Assure oil wettable surfaces for all interior areas contacting the fluids being evaporated or circulated, using zero water adsorbent materials (such as fluorocarbon resins) on heating surfaces, heater chamber interior, cascading baffles, and interior of flashing chamher; and lesser oil-wettable materials such as neoprene for interiors ofa hot oil-aqueous solution mixing chamher. and conditions between the evaporator tank and the heating chamber; also using substantially zero water adsorbent surfaces contacting the solids slurry throughout its flowsheet all aimed at trouble-free operation.

l2. Prevent solids crystalline growth on roughened surfaces or sharp edges, even though permanently oilwettable, by complete elimination of such surfaces or edges from the hot oil-aqueous solution mixing zone to the solids slurry settling zone in the flashing cascading chamber providing for more trouble-free operation than otherwise attainable.

l3. Assure a more efficient and less fouling operation with abundent surface exposure of liquid-vaporsolids mixture in the cascading chamber by cascading it downward over tiers of inverted, half cylinders which are preferentially oil wettable, and which contain no sharp edges or rough surface; which, further, permit removal of released vapors through their ends without recontacting them with the falling liquid.

14. Effect a smoother and more efficient operation by automatically and separately removing produced solids slurry and unevaporated aqueous solution as they accumulate.

15. Recycle the unevaporated aqueous solution, if required, admitting sufficient oil with the solution to prevent solids deposition on the preferentially oil wettable interiors of the pump and conduit for its recycling providing fouling-free operation.

16. Convey the unevaporated aqueous solution remainder, if required, to a second stage evaporator, injccting sufficient hot oil from this second stage into the solution as it leaves the 1st stage to prevent solids deposition on all conduit and controls interiors which are preferentially oil wettable.

I7. Remove mist of entrained oil suspended solids and aqueous solution from the vapor in a scrubber which contains no rough surfaces or sharp edges, and which is preferentially oil wettable to prevent adherence of solids and to assure trouble-free operation.

18. Effect multi-stage distillation of aqueous solution with sufficient control to permit separation of salts into various components in certain mineralized systems.

I9. Convey heat from a remote, and possibly dilute, source by circulating oil through such a source to adsorb heat, returning it to be mixed with aqueous solution for evaporation as herein disclosed; some of such heat sources being for example geothermal wells, subsurface terrestrial formations, and solar heat absorption devices thereby utilizing clean and in exhaustible sources of natural heat. Should heated oil temperatures be below atmospheric pressure evaporation temperature, subatmospheric pressures could be employed to effect evaporation using the afore-described methods.

20. Utilize an oil type liquid for the multi-purpose of conveying heat to an aqueous solution to be evaporated, wet the preferentially oil wettable surfaces of the confining system with a film to prevent adherence of solids and act as a vehicle to convey the suspended solids to a suitable settling zone offering the advantage of continuous, trouble-free operation.

21. Separate solids slurry into a saturated solution (for return to the system) and a damp solids product, using oil in the system of separation and handling to prevent adherence of solids to the preferentially oil wettable contacting surfaces thereby minimizing expensive shut-downs for cleaning.

22. Pre-heat the incoming raw aqueous solution, containing dispersed oil, with hot condensate product in a preferentially oil wettable heat exchanger thereby providing, continuous, maximum heat transfer without fouling of the surfaces.

DESCRIPTION OF THE INVENTION This apparatus and method are a novel approach to the evaporation of both saturated and unsaturated aqueous systems to any desired extent, including dryness. The water in the aqueous system may contain both dissolved and suspended solids, or only one or the other. Evaporation is effective without depositing any solids on any of the interior surfaces except those in the final settling zone from which they are removed as a slurry without caking to the surface supporting them.

The invention will be more readily understood by reference to the accompanying drawings and the following detail description. IN THE DRAWINGS:

FIG. I is a diagrammatic view of the heating and evaporating system as a whole and which includes a cascading vessel having various forms of cascading elements therein;

FIG. 2 is a detail view, partly in section and partly in elevation, of one of the cascading elements or members together with a supporting rod or tube suitably mounted within the cascading vessel;

FIG. 3 is a detail view of preferentially oil wettable hood which provides a roof over an oil quieting zone also mounted within the cascading vessel;

FIG. 4 is a further detail view of a perforated conical distribution hood mounted within the cascading vessel and which covers the cascading elements within such vessel; and

FIG. 5 is a detail view of one of the perforated portions of the conical distribution hood of FIG. 4.

Referring more particularly to the heating and evaporating system illustrated in the flow sheet (FIG. I) this system contains several principle elements namely a heater tank or vessel I a mixing chamber 2, and :1 cascading and evaporating tank or vessel 3 and suitable connections including inlet and outlet pipes, controls which will be more fully described hereinafter.

The heater tank or vessel I designed to preheat oil which may be mixed with inert gases, vapors and/or steam, supplied to the mixing chamber of the tank 2.

The preheater tank I contains a heat interchanger comprising an outer heater element 5 supported by a header 10. The heating element 5 is of thimble type and is coated inside and out with substantially zero water adsorbent material preferably of fluorinated hydrocarbon resin. Within the outer tube 5 is an inner tube 6 open at both ends and extending into the thimble tube 5 nearly to the bottom thereof and extending upwardly beyond the confines of the element 5. Hot steam or vapor is supplied to the heat exchanger 5 through pipe 7 and inert gas or steam is also supplied to the lower portion of the vessel 1 at 14 from a suitable source. Recirculated oil to be reheated is supplied at 12 under pressure from the cascading vessel 3 to be more fully described hereinafter. The oil supplied under pressure at the bottom of the tank 1 is passed upwardly through the tank or chamber and is heated by the heat exchanger 5, 6. The heated oil passes from the top of the chamber or tank I at 13 through pipe 14 to a horizontal mixing chamber 2 and is admixed therein with a highly dispersed aqueous solution in oil which enters the mixing chamber of tank 2 from pipe 45. The pipe 45 receives recirculated oil from the cascading an evaporator tank or chamber 3 and is being previously mixed with an aqueous solution by means of an oil-solution mixing pump 42. Other fluid connections leading to the pipe 45 will be described hereinafter. The fluids namely heated oil from the tank 1 and a highly dispersed aqueous solution in oil entering the mixing tank or chamber 2 at 15 and 46 respectively are mixed in such chamber and pass therefrom through outlet 17 and pipe 18 to the upper portion of the evaporator cascading tank or chamber 3. The material entering the tank 3 comprises a mixture of hot oil, vapor, unevaporated aqueous solution, inert gas and precipitated solids. The portion 19 of the pipe 18 extends through a hood-like conical member 73 into a discharge zone 19' and the hot fluids from the mixing tank 2 are discharged from outlet 19 onto a conical distributor hood 20 having perforations 20' therein as shown in FIGS. 1, 4 and 5. From the hood 20 the fluids pass over a series of sets of cascading members 21 supported on rods or tubes 22 (FIGS. 1 and 2) within the cascading chamber or zone 22. From the zone 22' the fluids pass over a sloping oil wettable hood 23 (FIGS. I and 3) which covers an oil quieting zone 33'. Within the cascading tank 3 a separation of oil, water, gases and solids takes place as will be more fully set forth hereinafter.

Vapors and gases are passed from the upper portion of the tank 3 at 24 into an entrained liquid scrubber 4 having a scrubber chamber 26 therein. Clean steam and other inert gas, if used, is removed from the scrubber chamber 26 through pipe 27 and oil suspended solids and aqueous solution from the separator are withdrawn at 28 and returned to the oil zone 31 of the 7 cascading tank 3 through pipe 29 entering the tank at 30.

Below the hood 23 there is disposed within the tank 3 an open-ended upright cylinder 34 into which extends an upturned outlet pipe 36 connected through conduit 37 and 39 with the lower end of the heater tank I through inlet 12 as previously described. A pump 38 provides positive pressure for the recirculated fluid passing through pipe 39.

A branch conduit 40 branching off the conduit 39 on the downstream side of pump 38 supplies a minor portion of the return oil from the evaporation tank 3 through a proportioning control valve 41 to a mixing pump 42, where the oil is mixed with re-cycled and make-up aqueous solution supplied through the proportioning control valve 51. The aqueous solution is dispersed into the oil with the oil acting as the outer phase of the dispersion. A valve 47 connected between the outlet and inlet sides of the mixing pump 42 provides a by-pass for the pump to recirculate oil from the pump outlet to pump inlet and insure violent mixing of the oil and water solution. The highly dispersed mixture of aqueous solution in oil from the mixing pump 42 is fed through the control valve 43 (governed by the tem peratue of the oil in zone 31 of tank 3) and conduit 45 into the mixing tank 2 at outlet 46.

The portion of aqueous solution stratified in zone 59 of evaporator tank 3 that is to be recycled is pumped from zone 59 of the tank 3 through outlet 53 by the pump 54 which is governed by probe 56 at the oil-water interface between oil zone 31 and water zone 59. A branch conduit connects the inlet side of pump 54 with the oil stratum zone 31 through outlet opening 55 and includes a hand set valve 2'. A portion of oil from zone 31 is mixed with aqueous solution from zone 59 at the inlet side of pump 54 for the ppurpose of prevention of solids adherence to the preferentially oil wettable surfaces provided in pump 54 and the circuit connected therewith. A conduit 57 connects the outlet side of pump 54 with a make-up aqueous solution conduit 50 at T-joint 58, and feeds recycled aqueous solution to the make-up aqueous solution conduit. Make-up aqueous solution is fed from a cold source 48' through a conduit into the heat exchanger 52' where it is heated by hot condensate fed in indirect heat exchange relationship through conduit 50" from a second stage evaporator, (not shown). A portion of the circulating oil from conduit 39 is fed through a hand set valve 49' and conduit 50' into the cold source feed line on the inlet side of heat exchange 52 where the oil is mixed with the make-up aqueous solution. This mixture of oil and aqueous solution is passed through zero water adsorbent tubes of heat exchanger 52, and out through conduit 48, through check valve 49 and through conduit 50 to join recycled aqueous solution as previously described. The cooled condensate from heat exchanger 52 is passed to storage (not shown) through conduit 51. All of the contacting interiors of the aforedescribed flow sheet are preferentially oil wettable to prevent adherence of solids.

The general construction and arrangement of the principal elements of the system have been briefly described and further elements and connections will be referred to in connection with an ennumeration of the principal steps of the process which will now be described.

STEP (l): Heating the Circulating Oil.

Heating a circulating, non-volatile oil-type liquid. still retaining a portion of solids and aqueous solution carryover from the evaporation and settling step, with a heating element 5, the surface of which is substantially zero water adsorbent and which is preferentially oil wettable in the presence of both oil and water. This heating element may utilize any source of heat such as vapor condensation, hot circulating fluids, combustion of gases, or electrical resistance. Since this invention includes a novel heat transfer tube arrangement, this is described in the drawing as the heating means for the circulating oil, utilizing heat from the condensation of vapor. This heating element raises the circulating oil temperature without deposition of any entrained solids from the oil on its zero water adsorbent surface which is constantly washed with the circulating oil. The fluorocarbon resins, particularly DuPonts Teflon type material called FEP with the technical name of hexafluoropropylenetetrafluoroethylene, have proved to be the most suitable zero water adsorbent coatings for surfaces requiring this property. Other initially oil wettable materials such as phenoilc and epoxy resins were tried as coatings on such heating elements while heating contaminated oil, but became water wettable in a few hours and permitted deposition of approximately A in. of said on the tube surface in 24 hours heating time. Only substantially zero water adsorbent surfaces such as DuPont FEP showed no trace of salt deposition on heating tubes in operation up to 400 hours. It is as-. sumed this condition should prevail indefinitely as it is well known there would be no chemical or physical change in the FEP fluorocarbon, and, most important, no water adsorption. in this step of heating the circulation oil I have found that the injection of steam or other preferably inert gas such as inert nitrogen greatly enhances the heat transfer through the heating tube wall to the oil. I have found that injecting approximately 1 part (by volume) gas to 4 parts oil increased the heat output of the tube as much as percent, where the gas was injected with the oil into the lower zone of a heating chamber. Steam is preferable to nitrogen for this use. since it passes out with the steam produced from the evaporation process, whereas nitrogen would require separation from the produced steam and recovering for re-use.

The details of step (1 are as follows: Warm oil, containing variable amounts of solids and aqueous solution carried over from settling zone (33') of tank (3) (see FIG. I) is conveyed through conduit (39) into the bottom of heater tank (I) at (12). Here it is mingled with inert gas or steam in zone (15') from source (12') through conduit (13') discharged at outlet (14'). This mixture of oil and gas flows upward in intimate contact with a heating element (5) which is coated with substantially zero water adsorbent material to prevent adherence of solids. The mixture of heated oil and gas leaves the top of heater tank (I) at outlet (13) passing through conduit (14) to a hot oil-aqueous solution mixing tank (2) at inlet (15). The particular novel heating tube depicted herein (FIG. 1) functions as follows: It utilizes heat liberated by condensation of a vapor, usually steam, though not restricted solely to steam. It consists of an outer thimble-type tube (5), attached at one end ofa header or tube sheet (10) with a heating vapor inlet (7). This thimble tube may be made of any metal suitable for the liquid to be heated, but in all cases must be coated with a substantially zero water adsorbent material, preferably a fluoronated hydrocarbon resin such as DuPont FEP. Inside this tube is a smaller tube (6), open at both ends, which is inserted relatively near the bottom of the thimble tube (5). This tube may be of the same material as the outer tube (5), or any other material, metal or otherwise, that is unaffected by the temperature and chemical nature of the condensing vapor. Its function is to remove all of the condensate as it is formed, with a minimum loss to vapor, automatically maintaining a liquid seal of condensate. Its diameter is such to permit passage of the maximum amount of condensate produceable under the operation conditions of the system. When the condensate level reaches inlet (8) of tube (6) and vapor attempts entry into the tube, resistance to flow of vapor immediately becomes sufficient to obstruct it, reestablishing the condensate liquid seal which prevents leak-by of appreciable amounts of vapor. Any slight loss of vapor due to a very minimum leak-by is justified by the non-mechanical simplicity of this liquid seal method which I believe to be novel and unique, and one which permits a design embodying a vertically disposed heating tube with one end unattached and free to expand and contract without becoming fouled with sediment. The condensed vapor leaves tube (6) at (9) to enter a condensate header (not shown) when multiple tubes are employed. Tube (6) is attached to tube sheet (9') which attaches to the outer tube (5) as shown, depicting a single tube arrangement. The annular space between tube (6) and the inner wall of tube (5) is filled with vapor completely to the condensate inlet (8) of tube (6), the vapor condensing in contact with tube (5). The inner surface of heater tube (5) may be coated with a fluorocarbon resin to promote dropwise condensation of the vapor, when it is steam, causing the condensate to trickle down the wall in streamlets, leaving more exposed surface to promote more efficient heat transfer through tube (5). This tube (5) is shown in a single arrangement, but may be composed of many such tubes as a bundle, being readily removeable from the top of heating chamber through flanged outlet 11). An auxiliary drain valve (16') is depicted at the bottom of tank (1), for manually bleeding off accumulated sludge, or simply draining the tank for any required purpose.

STEP (2): Reacting the Heated Oil With Aqueous Solution. (FIG. I).

After being heated, the circulating oil from tank (1) enters mixing tank (2) at and is then intimately mixed with aqueous solution (shown as a dispersion in oil in this disclosure), converting all or a portion of it to vapor. Since the total source of heat to vaporize the water must come from the heat of liquid of the oil, there must be a preponderance of oil to water. The initial temperature of the oil must be enough greater than the boiling temperature of the aqueous solution to provide a temperature drive through the oil and water interfacial films sufficient to effect boiling of the droplets of aqueous solution. The smaller the drops of aqueous solution and the more intimately they are mixed with the body of oil, the more readily and rapidly will they be converted to vapor. This is why it is preferable to premix the aqueous solution feed with a portion of the warm circulating oil, as shown in a mixing pump to promote a finely dispersed aqueous solution in the oil which functions as an outer phase and is very readily mixed, later, with the hot circulating oil in mixing chamber (2). The mixing of the aqueous solution or dispersion in oil with the hot oil in tank (2) may be effected in many conventional ways such as restriction of flow and subsequent expansion, baffling or tortuous flow, and is not described herein. I have found it very advantageous, however, to provide smooth contacting surfaces with no sharp edges, such surfaces being preferentially oil wettable, to prevent adherence of precipitated solids to the surfaces. Also, all passageways for the mixture, whether horizontal or vertical, prior to entry into the evaporator-cascading vessel (3), should be sufficiently restricted so that the velocity of the mixture will prevent any dropout of solids. Larger passageways and baffling as in tanks (2) and (3) should have substantially zero water adsorbent surfaces such as Du- Pont FEP, whereas smaller conduits such as (18) and (19) may be neoprene lined and still avoid deposition of precipitated solids. To illustrate the importance of oil wettable surfaces in this process: I have found that mixing hot oil with aqueous solution in a restricted, neoprene hose to produce steam and solids as the mixture flowed to a flash tank produced no deposition of salt on the hoseinterior, but that salt formed on the discharge end of the hose where the fabric insert in the hose was exposed to the discharging mixture. Trimming the end to a bevel eliminated the salt deposition on the water wettable fabric once it was removed. In this second step, the mixing of the hot oil and aqueous solution should be complete, although the extent of conversion of the solution to steam is quite variable, depending upon the time of exposure, the temperature of the oil, the ratio of oil to solution, and the pressure in the mixing system. I have found it preferable to evaporate only a portion of the aqueous solution in this mixing step, finishing the evaporation to the required extent in the combination flashing and cascading chamber (3) to be more fully described in forthcoming step (3). The final extent of aqueous solution evaporation in the whole system is governed by the amount of solution feed to a constant oil circulation rate with a constant temperature of the hot oil feed to the mixing tank, all in a fixed volume system. Some processes may require complete evaporation of the aqueous solution, whereas others may require a partial evaporation to promote removal of separate components of salts in succeeding stages of evaporation. This method and apparatus lends itself to either. The mixture of oil, vapor, solids, and unevaporated aqueous solution leaves tand (2) at (17), passes through conduit (18), then from discharge outlet (19) into tank (3), to step (3).

STEP (3): Flashing of Vapor, Vapor Removal and Further Evaporation by Cascading, Settling: (FIGS. 1, 2, 3, 4 & 5)

The mixture of hot oil, (cooled somewhat by the vaporization in step 2) vapor, precipitated solids, and unevaporated aqueous solution is discharged into vessel (3) where all interior parts and surfaces are coated with substantially zero water adsorbent material, vessel (3) functioning as follows:

a. Flashing vapor from the liquid mixture at outlet (19), vaporizing a portion of the remaining aqueous solution by discharge into zone (19) at a lower pressure. This vapor is removed from zone (19'), with partial scrubbing of any fine, entrained liquid droplets with a hood-like cone (73) which is coated on both sides with a zero water adsorbent material. This vapor then joins other removed vapor at (24) to leave, vessel (3) through conduit (25) to final scrubber (4) at zone (26). The clean vapor (and inert gas if otherthan steam was used for injection into vessel (1)) leaves scrubber (4) to be condensed or used for heating in the next evaporation stage. The removed oil suspended solids and aqueous solution leaves tank (4) at outlet (28) to return to oil zone (31) of tank (3) through conduit (29) at inlet (30). This scrubber (4) can be one of many designs, but it should have all interior surfaces coated with zero water adsorbent material, with no sharp edges, rough surfaces or pockets for solids accumulation.

b. Removing the remainder of the vapor from the foaming oil-aqueous solution-solids mixture by passing it through the perforated conical distribution hood (20) FIGS. 1 & 4 which is zero water adsorbent on both sides, downward over zero water adsorbent downward sloping surfaces of members (21) and (22) (FIGS. 1 & 2) which have no sharp edges, no rough surfaces and no pockets to catch solids.

c. Evaporating a further portion of the aqueous solution entrained in the still hot oil as the mixture is subjected to additional exposure as thin moving layers on cascading surfaces of members (21) and (22) and falls in sheets and streamlets from one tier of cascading members to the next.

(1. 1n the design depicted showing cascading members (21) which are inverted half cylinders supported by smaller rods or tubes (22) with all surfaces zero water adsorbent, water vapors pass up under the inside surface of the hollow, inverted half cylinders (21) and out at each end, thereby avoiding remixing with the cascading liquid mixture. The preferentially oil wettable undersurface of the half cylinder scrubs out contacting oily mist and lesser water content, rejoining it with the downward moving body of liquid that spills over the sides of the inverted half cylinders.

e. The oil, precipitated solids and any remaining aqueous solution mixture leaves the cascading zone (22') with substantially all entrained vapor removed, and with sufficient reduction in temperature that no further evaporation of aqueous solution is possible. It flows over a sloping, preferentially oil wettable hood (23) (FIGS. 1 8; 3) which provides a roof over oil quieting zone (33') and which directs the mixture to the outer periphery of vessel (3) to settling zone (31). Zone (31 just below foam zone (32) is an aqueous solution and solids drop out zone for the oil from whence the oil moves at (33) to quieting zone (33') created by open ended vertical cylinder (34). The remainder aqueous solution drops out of oil settling zone (31) to zone (59), the solids slurry dropping on downward to conical zone (63) at the bottom of tank (3).

STEP (4): Disposition of Oil and Unevaporated Aqueous Solution From Vessel (3):

a. Oil, with most of the aqueous solution and solids removed from it, in quieting zone (33') is removed from vessel (3) through overflow outlet pipe (36) and through conduit (37) to a pump (38) which recirculates it through conduit (39) to heating vessel (1) at zone All of the contacting surfaces for the returning oil from tank (3) to tank (1) should be preferentially oil wettable, though not neccessarily zero water adsorbent. Not having a circulating pump (38) available with oil wettable interiors, I used a small gear pump with bronze trim in my preliminary tests. In 48 hours, salt depositions caused seizure of the rotors. I found that injecting fresh water just ahead of the pump suction in a ratio as small as 1 part water to 3200 parts of oil completely eliminated seizure in the pump. The alternative to my novel preferentially oil wettable surfaces for this return oil circuit would be the provision of 100 percent clean oil, a procedure which would be both difficult and expensive.

b. A very minor. portion of the return oil from the cascading vessel (3) through pump (38) is sent through proportioning control valve (41) from outlet (40) of conduit (39). This oil is mixed in mixing pump (42) with recycled and make-up aqueous solution which come through proportioning valve (51), and are dispersed into the oil with the oil acting as the outer phase of the dispersion. Valve (47) acts as a bypass for the mixing pump (42) to discharge and pump back into its own suction to assure violent mixing in the pump. The feed of oily dispersion is fed through control valve (43), governed by the temperature of the oil in zone (31) of tank (3), through conduit (45) to mixing tank (2) at outlet (46). The portion of dropped out aqueous solution in zone (59) of tank (3) that is to be recycled leaves zone (59) at outlet (53) to pump (54) which is governed by probe (56) at oil-outlet interface between oil zone (31) and water zone (59). A portion of oil from zone (31 leaves at (55) through a hand set valve (2') to join aqueous solution moving to pump (54), for the purpose of preventing solids adherence to all preferentially oil wettable surfaces in this circuit. This mixture of oil and recycled aqueous solution passes through conduit (57) to join pre-heated oily, make-up aqueous solution at (58) and proceeds to proportioning control valve (51) as previously described. The makeup aqueous solution from cold source (48') is mixed with a portion of the circulating oil which is supplied from conduit (39) through hand set valve (49') through conduit (50). This oily mixture of cold aqueous solution passes through zero water adsorbent tubes of heat exchanger (52'), being heated by hot condensate from source (50') from the 2nd stage evaporator, and out through conduit (48) through check valve (49) through conduit (50) to join recycled aqueous solution as previously described. The cooled condensate from heat exchanger (52') passes to storage from (51'). All of the contacting interiors of the aforedescribed flowsheet are preferentially oil wettable to prevent adherence of solids.

c. If the process involves more than one stage of evaporation, and none of the unevaporated portion of aqueous solution is to be recycled, then it would be removed from zone (59) of vessel (3) at outlet (66) through valve (67) controlled by probe (68) at the oilwater interface between zones (31) and (59), being mixed with oil at junction (72), this oil coming from the second stage at (70) and fed by pump (71) which is hand regulated, the purpose of this oil to prevent adherence of solids to preferentially oil wettable surfaces in passing from (66) to 2nd stage. The oily aqueous so lution leaves control valve (67) to pass through conduit (69) to become make-up feed for the second stage of its evaporation.

When recycling aqueous solution the probe 56 senses the interface between the oil in zone 31 and the aqueous solution in zone 59 and controls the pump 54-to increase or decrease the volume of solution pumped from zone 59 in order to maintain the oil-aqueous solution interface level substantially constant. M

When passing the aqueous solution to a second stage evaporator the probe 68 senses the interface between the oil in zone 31 and the aqueous solution in zone 59 and controls the valve 67 to regulate the outflow of aqueous solution from the zone 59 in order to maintain the oil-aqueous solution interface level substantially constant.

Probe 65 responds to a difference in density between the aqueous solution and the solids slurry in zone 63 to regulate the control valve 64 permitting the removal of solids slurry from the botton of evaporator tank 3 as it accumulates in zone 63.

Probe 44 is a temperature responsive probe which regulates the flow of oil-aqueous solution dispersion through valve 43 in order to decrease the flow of the dispersion as the temperature in zone 31 drops and increases the flow of the dispersion as the temperature in zone 31 rises.

Probes 44, 56, 65 and 68 are all commerically available probes which can be more fully described if necessary, but are not part of the present invention.

STEP Disposition of Solids Slurry From Zone (63) of Vessel (3):

The solids slurry is removed from the bottom of the cone of vessel (3) from zone (63) through control valve (64) which is governed by probe (65) which in turn is governed by the density of the slurry. lf sufficient oil is not occluded in the settling slurry in zone (63), supplemental oil may be supplied from the second stage evaporator through hand controlled valve (68') through conduit (69') to slurry zone (63), this oil being supplied by a pump (not shown). This oil is required to prevent adherence of solids to the totally preferentially oil wettable surfaces contacting the slurry from its departure from zone (63) to the final destination of the separated products. The slurry passes through control valve (64) through pump (65') to a solids-liquid separator, in this disclosure depicted as a liquid cyclone (64'). In this separator it is separated into a damp solids product which goes to storage or further drying at (66') and aqueous solution-oil mixture which leaves the separator at (67') to pass to the second stage, or back to aqueous solution zone of tank (3) (not shown) if the system is a single stage evaporator.

FIG. 2 depicts a cross-sectional detail of half-cylinder cascading member (21) and support rod or pipe (22). Both (21) and (22) are externally coated with zero water adsorbent material, usually a fluorocarbon resin to prevent adherence of solids to their surfaces. The support rod (22) size is governed by the load it must bear and the diameter of the vessel (3), all calculable by those skilled in the art. All surfaces of (21) must be smooth, with no sharp edges for solids deposition and growth, and made of any material suitable for the aqueous solution being evaporated and capable of withstanding bonding temperatures of the oil wettable coating. such as metal or plastic.

FIG. 3 is a cross-section of conical hood (23) of similar material as (21), with smooth surfaces, no sharp edges and preferentially oil wettable.

FIGS. 4 and 5 are details of a perforated distributor cone for uniformly introducing the liquid mixture to the top of the cascading tiers composed of half cylinders (21). Its size and perforation size are governed by the volume of liquid to be handled and the crosssectional size of the cascading pile. It is coated similarly to (21) and (23). with no sharp edges or rough surfaces. The perforations (20') are shown in detail in FIG. 5, and project as teats downwardly to assure the liquid will leave the holes as streamlets, rather than adhere to the oil-wettable underside of the cone, flowing down its surface. The teatlike perforations are smooth, with no sharp edges.

In the present specification and claims reference is made to an immiscible liquid" or "oil. which is temporarily intimately mixed or dispersed, as by agitation, pressure or the like with an aqueous solution to be heated to remove impurities therefrom. Such immiscible liquid or oil while preferably a hydrocarbon need not necessarily be a true hydrocarbon but may be any liquid preferably organic which is immiscible with the aqueous liquid containing impurities to be removed. The particular immiscible liquid or oil to be employed depends on the aqueous liquid to be treated though there may be wide variations dependent on the availability of the liquid and the particular conditions under which the process is to be carried out. For example in treating brine I have found mineral oils such as automo bile lubricating oils, turbine oils and the like to be particularly satisfactory and these have actually been used in the process herein described. The turbine oils have been found to be stable and not readily oxidizable on heating. For refining vegetable materials such as beet sugar solutions or the like a non-toxic mineral or vegetable oil may be used. Where a high degree of heat stability is required a heat resistant oil such as silicone fluids or silanes may be employed and are contemplated as intended to be included under the terms immiscible liquid and oil as used in the present specification and claims.

The oil or immiscible liquid should be of different specific gravity and of higher boiling point than the aqueous solution with which it is to be temporarily mixed. Mineral oils, vegetable oils, silicone fluids and silanes are well known products are are defined for example in Reinholds The Condensed Chemical Dictionary, 6th Edition.

It will be understood that by the term immiscible as used in the present specification and claims a permanent mixture is referred to since the immiscible liquid or oil on the one hand and the aqueous solution on the other hand cannot be permanently mixed but one may be temporarily mixed or dispersed in the other as by the aid of pressure, agitation or the like and such temporary mixture or dispersion may thereafter be separated by suitable means as is well known in the art.

What is claimed is:

l. The improvement in the method of evaporating an aqueous solution containing dissolved solids to prevent adherence of precipitated solids to the contacting surface of the apparatus in which the method is carried out; which improvement consists in that the evaporation of the solution takes place in apparatus whose hot contacting surface is preferentially oil wettable and substantially zero adsorbent of water from the solution while continuously wetting the contacting surface with an organic liquid which is immiscible with the aqueous solution being evaporated. said contacting surface comprising a fluorocarbon polymer.

16 mineral oils. vegetable oils, silicone fluids and silanes. 5. The invention as defined in claim 1 wherein the fluorocarbon polymer is hexafluoropropylenetetrafluoroethylene.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 333 91.395 Dated June 24 107 Inventor 5) Ra ns ome 'aJ 11in It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the abstract, paragraph 2, line 1 should read as follows:

"All contacting; apparatus surtaces exposed to the---'* Signed and Scaled this eighteenth D 3y Of November 1 9 75 [SEAL] A nest:

RUTH C MASON C. MARSHALL DANN :HHSIHIX UJ/HW ('mmmsswm'r n! Pan-n15 and Trade/"(NM 

1. THE IMPROVEMENT IN THE METHOD OF EVAPORATING AN AQUEOUS SOLUTION CONTAINIG DISSOLVED SOLIDS TO PREVENT ADHERENCE OF PRECIPITATED SOLIDS TO THE CONTRACTING SURFACE OF THE APPARATUS IN WHICH THE METHOD IS CARRIED OUT; WHICH IMPROVEMENT CONSISTS IN THAT THE EVAPORATION OF THE SOLUTION TAKES PLACE IN APPARATUS WHOSE HOT CONTACTING SURFACE IS PREFERENTIALLY OIL WETTABLE AND SUBSTANTIALLY ZERO ADSORBENT OF WATER FROM THE SOLUTION WHILE CONTINUOUSLY WETTING THE CONTACTING SURFACE WITH AN ORGANIC LIQUID WHICH IS IMMISCIBLE WITH THE AQUEOUS SOLUTION BEING EVAPORATED, SAID CONTACTING SURFACE COMPRISING A FLUOROCARBON POLYMER.
 2. The invention as defined in claim 1 wherein the immiscible liquid is a hydrocarbon oil.
 3. The invention as defined in claim 1 wherein the immiscible liquid is a mineral oil.
 4. The invention as defined in claim 1 wherein the immiscible liquid is selected from a group consisting of mineral oils, vegetable oils, silicone fluids and silanes.
 5. The invention as defined in claim 1 wherein the fluorocarbon polymer is hexafluoropropylenetetrafluoroethylene. 